Prof Long had conducted some profound research on animal and human psychology, including some on children, as well as experimental and nervous psychology. He has also compiled a number of dictionaries on animals and plants. Many of his works had won literature and art awards. The works included photo dictionaries on fruits, roots and plants.

"Many of Long's objects are very useful to students and researchers who are studying psychology of human and animal behaviour and the development of biology in Viet Nam," Huy said.

Born into a royal family in 1925, Long, a revolutionary turned intellectual, had met with many obstacles including his family background which prevented him from going abroad (at that time, to the Soviet Union) to do a master's.

Before Viet Nam launched its doi moi (renewal) policy, and without such a title he could easily have been pushed out of the scientific community, he recalled.

Fortunately, thanks to an initiative of the Rector of the Ha Noi Pedagogy University (HNPU), Nguyen Canh Toan, Long could start working on his thesis in Viet Nam itself.

In 1970, Long was among the first three candidates MA degree in the country.

Long's thesis "A Number of Initial Data on Psychology-ecology of Tamed African Carp" had received high appreciation from his colleagues.

Long recalled that despite fierce fighting during the American War in the country, "the university held a big ceremony for me to defend my MA thesis."

Over 100 scientists, including professors Dao Van Tien, Le Kha Ke and Thai Van Trung, the first Vietnamese to successfully complete his PhD thesis in the Soviet Union, were present at the university's auditorium.

Long's thesis had received favourable remarks from most people there, but he was shocked when Dr Dang Thu, who owned the highest title in the country on psychology at that time, raised an objection.

Thu pointed out to 19 pages in Long's thesis that contained, what he believed, was false information. In addition, an opposing group of the Dinh Bang Marine Research Station revealed a further nine incorrect points in Long's thesis.

Thu said he had discovered Long's incorrect data and asked him where he had got it from. Long had to reply or he would have been accused of fabricating the data.

"I agreed with Dr Thu's remarks on my data," he recalled, and then began explaining his findings to everyone present there.

Long said that while researching the carp, he noted the temperature in the water that was one metre below the pond's surface. During the monsoon, temperature in the air was often cooler than the temperature in the water which often took 5 to 10 hours to cool.

When the rain stopped, air temperature was warmer for a longer time, and then the temperature in the water got warmer, he explained.

There was a moment's silence in the lecture hall. Then suddenly everyone began laughing loudly and there was resounding applause from those who were attending.

After having defended his MA thesis, Long compiled over 100 books on popular biology topics and texts apart from other subjects.

"Long's teaching methods were special and unique. He always gave examples to draw out the curious students and tap their creativity. Owing to such methods that we understand our subject so well," Prof Dr Tran Kien, former head of the HNPU's Biology Department, said.

"His interesting teaching methods have led us from discovery to discovery, and I could say that my teacher has reached the peak of the teaching art," Kien added.

The head of Animal Subjects at the University of Agriculture, Prof Dr Phan Trong Cung, recalled, "Teacher Long's lifestyle and thinking has influenced me a lot. I've learned how to 'diagramise' a lesson from him. When I started teaching, my students found it easy to understand me."

"When so many of my local and foreign students showed interest in attending my lectures, I told them I had followed my beloved teacher Long's methods," said Cung.

Associate Prof Dr Mai Sy Tuan, head of the current HNPU's Biology Department, said he himself had been taught by Long.

"I was very impressed with my teacher's book Hoa dien va Phan xa tri nho. I don't exactly know whether it is a scientific curriculum or an art work because of its simple and attractive explanation. But it is very profound and has helped us easily understand the most difficult content in the subject. Maybe, that is because of our teacher's excellent teaching ability."

"More than 40 years have passed, but I still remember teacher Long's lecturing methods. They became effective guidelines for me to teach my students later," Tuan said.

"Despite educationists saying again and again that we have to innovate, for me, teacher Long's methods could never be changed because his way of teaching was like a dream for numerous lecturers like us," he added.

Apart from teaching in Viet Nam, Long has taught at other universities in Laos, Cambodia and Madagascar.

He has been a director at the Information Centre for Transferring Advanced Biology of Viet Nam, pedagogic advisor of the French Government and international organisations of French teaching (AUPELF-UREF) which later became the Agence universitaire de la Francophonie.

His main works include Hoa dien va phan xa tri nho (1973), and A World of Things for You (5 episodes). — VNS